1. Field of the Invention
The present invention relates to wireless networks and more particularly, to timer synchronization in network nodes of wireless networks.
2. Description of the Related Art
Generally, various methods are used to synchronize timers between a data transmitter and a data receiver in a wireless network. Timers are used to time the processing of data transmitted/received in a data protocol object (e.g., frame, superframe, and the like). When the data are transmitted between entities executing the same data handling protocol, timers are synchronized using the same protocol; however, it is difficult to synchronize timers when the data are transmitted between entities executing different data handling protocols. A mediation or protocol interpretation scheme is required to communicate control information including the timer synchronization between the two entities executing different data handling protocols. One such mediation/protocol interpretation scheme is the Protocol Adaptation Layer (PAL) specified by the 1394SM Trade Association in various working drafts, which are incorporated herein by reference in their entirety for all purposes.
The PAL mediates between a higher layer of a first protocol and a lower layer of a second protocol. The PAL mimics the behavior of the higher layer when transferring data objects from the lower layer to the higher layer. Similarly, the PAL mimics the behavior of the lower layer when transferring data objects from the higher layer to the lower layer. Typically, the PAL enables an application developed using the IEEE 1394 protocol to be adapted to another application developed using the IEEE 802.15.3 protocol. The IEEE 1394 protocol defines a universal interconnect bus for interconnecting a variety of consumer electronic devices and the IEEE 802.15.3 protocol defines a high rate Wireless Personal Area Network (WPAN) which enables connectivity between the variety of consumer electronic devices within a personal operating space. The PAL enables a virtual 1394 bus within an IEEE 802.15.3 piconet.
Typically, in a piconet, one device is designated as a network coordinator. The network coordinator is responsible to admit or exclude devices (nodes) that attempt to connect to the virtual 1394 bus within its piconet. The network coordinator periodically broadcasts bus and cycle timing information to all the nodes operating within the piconet to distribute accurate bus and cycle times for data interpretation by each node. Each node includes cycle timers, which are synchronized with the cycle time broadcast by the coordinator. The cycle timers are used to guarantee a constant delay for the transfer of data objects between two nodes. The cycle timers drift over time relative to one another and require synchronization to avoid delay jitter, receive buffer overflow/under run, and the like.
The PAL protocol defined by the 1394SM Trade Association specifies a method of synchronizing the cycle timer. The method includes sampling a master timer (e.g., the cycle timer of a network coordinator) at the start time of a first beacon and broadcasting the sampled master timer value in a second beacon. The method further requires sampling a slave timer (e.g., the cycle timer of a data transmitting or receiving node) at the start of the first beacon and determining a difference between the sampled master timer value and the sampled slave timer value during the processing of the second beacon. The method uses the difference to correct the cycle time of the slave timer. This method causes the slave timer to oscillate when the master and slave timers have different initial values or when a beacon is not received correctly by the node containing the slave timer. Further, this method also requires correctly receiving two consecutive beacons to synchronize the master and slave timers. Accordingly, an effective method is needed to synchronize timers in a wireless network.